It has been known in the prior art of exposed shackle padlocks to provide shackle assemblies for which a reciprocating movement between the shackle and the lock housing is required to open the padlock. The most common form of these padlocks comprises a relatively complex arrangement of locking members to latch and release the shackle relative to the padlock body. These padlocks have an inverted J-shaped shackle that when released, moves upwardly out of the body to achieve relative reciprocal movement. The short end of the shackle will then pivot to open only after vertically clearing the padlock body, and the long end is entrained in the locking mechanism. These type of padlocks are generally called reciprocating shackle padlocks.
Another variation on this theme of relative reciprocal movement between the shackle and the padlock body is a reversal of parts as shown in Atkinson, U.S. Pat No. 3,837,189 issued Sept. 24, 1974. The Atkinson design padlock comprises an inverted U-shaped shackle with one end fractionally shorter than the other, and a lock body having an outer shell and an inner core which are adapted to move a constrained amount relative to each other. When the locking mechanism is actuated to an "open" position, the shorter end of the shackle is released by downward movement of the outer shell. This permits the shackle to pivot open.
One serious problem with reciprocating padlocks is that internal space limitations do not provide a sufficiently deep recess for the free end of the shackle. Due to the inherent play in the lock mechanism in securing the entrained end of the shackle, the shackle often can be pulled out a sufficient distance to clear the upper end of the padlock body to be pivoted open. There is nothing to prevent the shackle from pivoting once it clears the upper surface of the padlock body. The force necessary to open some padlocks is as little as 140 lbs; many high school-age young men can pull open such locks easily by hand.
Another disadvantage of many current padlocks is the use of rotary dials. Rotary dials can not be used in the dark or by many handicapped or visually impaired people. Often, dexterous fully-sighted persons have difficulty opening such locks, even in daylight. In addition, rotary dial operation is slow and requires relative precision of alignment of the dial markings with the index, and the settings are imprecise in all but the most expensive locks.
There are also disadvantages with the use of key locks. Keys are an inconvenience to carry around and can be easily lost or stolen. Most people would prefer to keep a combination in their head rather than to add another key to their key ring.
Push-button locks, such as Cheng, U.S. Pat. No. 4,751,830, issued June 21, 1988, have significant advantages over rotary dial and key locks. The positive action of a push-button lock allows for quick, easy and accurate operation. They offer the relative pick-resistance of combination locks, and also can be opened in the dark, or by sightless, visually impaired or physically handicapped persons.
One disadvantage with current push-button padlocks is the amount of internal parts required which results in a padlock that is complex to assemble. Another disadvantage is that some reciprocating shackle push-button padlocks are susceptible to being opened by a small prying forces as a result of the inherent amount of play in an exposed shackle, reciprocating padlock. Still another disadvantage with some push-button padlocks is that the buttons, as in Cheng, pass completely through the locks and do not reset themselves. Thus the combination can be observed while open, and care must be taken by the user to push all the buttons one way or the other (all to the front or all to the back) so as to disguise the combination and relock the lock. Further, such nonauto reset (relock) locks are not adaptable to deadbolt or cabinet lock usage, as the rear of the lock must be exposed for manual resetting of the buttons. In a deadbolt or cabinet type (mounted or inset) lock, the lock is mounted with the back inset, flush or abutting a carrying member, such as a door, door jamb, frame, casing or the like, and accordingly is not accessible for resetting the buttons. While some push button combination locks, particularly door locks, are available, they are typically very expensive or complex electronic locks dependent on fallible electric power.
Accordingly, there is a need in the art for a strong, autoreset push-button lock that is easy to operate, inexpensive to assemble, has a simplicity that does not yield excessive play permitting opening by a small prying force, and is equally adaptable to use either in a padlock or deadbolt form.